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如何實現(xiàn)定時推送的具體方案

更新時間：2021年04月19日 17:33:40 作者：dotNet源計劃

在工作當(dāng)中遇到了一個需要定時向客戶端推送新聞、文章等內(nèi)容。小項目又用不了大框架,這個時候在網(wǎng)上搜了很久沒有找到合適的解決方案,直到看到了一位大佬寫的文章提供了一個非常不錯的思路本篇文章也是受到他的啟發(fā)實現(xiàn)了之后這里分享給大家

詳細內(nèi)容

詳細內(nèi)容大概分為4個部分，1.應(yīng)用場景 2.遇到問題 3.設(shè)計 4.實現(xiàn) 5.運行效果

1.應(yīng)用場景

需要定時推送數(shù)據(jù)，且輕量化的實現(xiàn)。

2.遇到問題

如果啟動一個定時器去定時輪詢
（1）輪詢效率比較低
（2）每次掃庫，已經(jīng)被執(zhí)行過記錄，仍然會被掃描（只是不會出現(xiàn)在結(jié)果集中），會做重復(fù)工作
（3）時效性不夠好，如果每小時輪詢一次，最差的情況下會有時間誤差
如何利用“延時消息”，對于每個任務(wù)只觸發(fā)一次，保證效率的同時保證實時性，是今天要討論的問題。

3.設(shè)計

高效延時消息，包含兩個重要的數(shù)據(jù)結(jié)構(gòu)：

環(huán)形隊列，例如可以創(chuàng)建一個包含3600個slot的環(huán)形隊列（本質(zhì)是個數(shù)組）
任務(wù)集合，環(huán)上每一個slot是一個Set

同時，啟動一個timer，這個timer每隔1s，在上述環(huán)形隊列中移動一格，有一個Current Index指針來標識正在檢測的slot。

Task結(jié)構(gòu)中有兩個很重要的屬性：

Cycle-Num：當(dāng)Current Index第幾圈掃描到這個Slot時，執(zhí)行任務(wù)
Task-Function：需要執(zhí)行的任務(wù)指針

假設(shè)當(dāng)前Current Index指向第一格，當(dāng)有延時消息到達之后，例如希望3610秒之后，觸發(fā)一個延時消息任務(wù)，只需：

計算這個Task應(yīng)該放在哪一個slot，現(xiàn)在指向1，3610秒之后，應(yīng)該是第11格，所以這個Task應(yīng)該放在第11個slot的Set中
計算這個Task的Cycle-Num，由于環(huán)形隊列是3600格（每秒移動一格，正好1小時），這個任務(wù)是3610秒后執(zhí)行，所以應(yīng)該繞3610/3600=1圈之后再執(zhí)行，于是Cycle-Num=1

Current Index不停的移動，每秒移動到一個新slot，這個slot中對應(yīng)的Set，每個Task看Cycle-Num是不是0：

如果不是0，說明還需要多移動幾圈，將Cycle-Num減1
如果是0，說明馬上要執(zhí)行這個Task了，取出Task-Funciton執(zhí)行（可以用單獨的線程來執(zhí)行Task），并把這個Task從Set中刪除

使用了“延時消息”方案之后，“訂單48小時后關(guān)閉評價”的需求，只需將在訂單關(guān)閉時，觸發(fā)一個48小時之后的延時消息即可：

無需再輪詢?nèi)坑唵危矢?/li>
一個訂單，任務(wù)只執(zhí)行一次
時效性好，精確到秒（控制timer移動頻率可以控制精度）

4.實現(xiàn)

首先寫一個方案要理清楚自己的項目結(jié)構(gòu)，我做了如下分層。

Interfaces ，這層里主要約束延遲消息隊列的隊列和消息任務(wù)行。

public interface IRingQueue<T>
{
    /// <summary>
    /// Add tasks [add tasks will automatically generate: task Id, task slot location, number of task cycles]
    /// </summary>
    /// <param name="delayTime">The specified task is executed after N seconds.</param>
    /// <param name="action">Definitions of callback</param>
    void Add(long delayTime,Action<T> action);
    /// <summary>
    /// Add tasks [add tasks will automatically generate: task Id, task slot location, number of task cycles]
    /// </summary>
    /// <param name="delayTime">The specified task is executed after N seconds.</param>
    /// <param name="action">Definitions of callback.</param>
    /// <param name="data">Parameters used in the callback function.</param>
    void Add(long delayTime, Action<T> action, T data);
    /// <summary>
    /// Add tasks [add tasks will automatically generate: task Id, task slot location, number of task cycles]
    /// </summary>
    /// <param name="delayTime"></param>
    /// <param name="action">Definitions of callback</param>
    /// <param name="data">Parameters used in the callback function.</param>
    /// <param name="id">Task ID, used when deleting tasks.</param>
    void Add(long delayTime, Action<T> action, T data, long id);
    /// <summary>
    /// Remove tasks [need to know: where the task is, which specific task].
    /// </summary>
    /// <param name="index">Task slot location</param>
    /// <param name="id">Task ID, used when deleting tasks.</param>
    void Remove(long id);
    /// <summary>
    /// Launch queue.
    /// </summary>
    void Start();
}
 public interface ITask
 {
 }

Achieves，這層里實現(xiàn)之前定義的接口，這里寫成抽象類是為了后面方便擴展。

using System;
using System.Collections.Concurrent;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using DelayMessageApp.Interfaces;
namespace DelayMessageApp.Achieves.Base
{
public abstract class BaseQueue<T> : IRingQueue<T>
{
    private long _pointer = 0L;
    private ConcurrentBag<BaseTask<T>>[] _arraySlot;
    private int ArrayMax;
    /// <summary>
    /// Ring queue.
    /// </summary>
    public ConcurrentBag<BaseTask<T>>[] ArraySlot
    {
        get { return _arraySlot ?? (_arraySlot = new ConcurrentBag<BaseTask<T>>[ArrayMax]); }
    }
    public BaseQueue(int arrayMax)
    {
        if (arrayMax < 60 && arrayMax % 60 == 0)
            throw new Exception("Ring queue length cannot be less than 60 and is a multiple of 60 .");
        ArrayMax = arrayMax;
    }
    public void Add(long delayTime, Action<T> action)
    {
        Add(delayTime, action, default(T));
    }
    public void Add(long delayTime,Action<T> action,T data)
    {
        Add(delayTime, action, data,0);
    }
    public void Add(long delayTime, Action<T> action, T data,long id)
    {
        NextSlot(delayTime, out long cycle, out long pointer);
        ArraySlot[pointer] =  ArraySlot[pointer] ?? (ArraySlot[pointer] = new ConcurrentBag<BaseTask<T>>());
        var baseTask = new BaseTask<T>(cycle, action, data,id);
        ArraySlot[pointer].Add(baseTask);
    }
    /// <summary>
    /// Remove tasks based on ID.
    /// </summary>
    /// <param name="id"></param>
    public void Remove(long id)
    {
        try
        {
            Parallel.ForEach(ArraySlot, (ConcurrentBag<BaseTask<T>> collection, ParallelLoopState state) =>
            {
                var resulTask = collection.FirstOrDefault(p => p.Id == id);
                if (resulTask != null)
                {
                    collection.TryTake(out resulTask);
                    state.Break();
                }
            });
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
        }
    }
    public void Start()
    {
        while (true)
        {
            RightMovePointer();
            Thread.Sleep(1000);
            Console.WriteLine(DateTime.Now.ToString());
        }
    }
    /// <summary>
    /// Calculate the information of the next slot.
    /// </summary>
    /// <param name="delayTime">Delayed execution time.</param>
    /// <param name="cycle">Number of turns.</param>
    /// <param name="index">Task location.</param>
    private void NextSlot(long delayTime, out long cycle,out long index)
    {
        try
        {
            var circle = delayTime / ArrayMax;
            var second = delayTime % ArrayMax;
            var current_pointer = GetPointer();
            var queue_index = 0L;
            if (delayTime - ArrayMax > ArrayMax)
            {
                circle = 1;
            }
            else if (second > ArrayMax)
            {
                circle += 1;
            }
            if (delayTime - circle * ArrayMax < ArrayMax)
            {
                second = delayTime - circle * ArrayMax;
            }
            if (current_pointer + delayTime >= ArrayMax)
            {
                cycle = (int)((current_pointer + delayTime) / ArrayMax);
                if (current_pointer + second - ArrayMax < 0)
                {
                    queue_index = current_pointer + second;
                }
                else if (current_pointer + second - ArrayMax > 0)
                {
                    queue_index = current_pointer + second - ArrayMax;
                }
            }
            else
            {
                cycle = 0;
                queue_index = current_pointer + second;
            }
            index = queue_index;
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
            throw;
        }
    }
    /// <summary>
    /// Get the current location of the pointer.
    /// </summary>
    /// <returns></returns>
    private long GetPointer()
    {
        return Interlocked.Read(ref _pointer);
    }
    /// <summary>
    /// Reset pointer position.
    /// </summary>
    private void ReSetPointer()
    {
        Interlocked.Exchange(ref _pointer, 0);
    }
    /// <summary>
    /// Pointer moves clockwise.
    /// </summary>
    private void RightMovePointer()
    {
        try
        {
            if (GetPointer() >= ArrayMax - 1)
            {
                ReSetPointer();
            }
            else
            {
                Interlocked.Increment(ref _pointer);
            }
            var pointer = GetPointer();
            var taskCollection = ArraySlot[pointer];
            if (taskCollection == null || taskCollection.Count == 0) return;
            Parallel.ForEach(taskCollection, (BaseTask<T> task) =>
            {
                if (task.Cycle > 0)
                {
                    task.SubCycleNumber();
                }
                if (task.Cycle <= 0)
                {
                    taskCollection.TryTake(out task);
                    task.TaskAction(task.Data);
                }
            });
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
            throw;
        }
    }
}
}
using System;
using System.Threading;
using DelayMessageApp.Interfaces;
namespace DelayMessageApp.Achieves.Base
{
public class BaseTask<T> : ITask
{
    private long _cycle;
    private long _id;
    private T _data;
    public Action<T> TaskAction { get; set; }
    public long Cycle
    {
        get { return Interlocked.Read(ref _cycle); }
        set { Interlocked.Exchange(ref _cycle, value); }
    }
    public long Id
    {
        get { return _id; }
        set { _id = value; }
    }
    public T Data
    {
        get { return _data; }
        set { _data = value; }
    }
    public BaseTask(long cycle, Action<T> action, T data,long id)
    {
        Cycle = cycle;
        TaskAction = action;
        Data = data;
        Id = id;
    }
    public BaseTask(long cycle, Action<T> action,T data)
    {
        Cycle = cycle;
        TaskAction = action;
        Data = data;
    }
    public BaseTask(long cycle, Action<T> action)
    {
        Cycle = cycle;
        TaskAction = action;
    }
    public void SubCycleNumber()
    {
        Interlocked.Decrement(ref _cycle);
    }
}
}

Logic，這層主要實現(xiàn)調(diào)用邏輯，調(diào)用者最終只需要關(guān)心把任務(wù)放進隊列并指定什么時候執(zhí)行就行了，根本不需要關(guān)心其它的任何信息。

public static void Start()
{
    //1.Initialize queues of different granularity.
    IRingQueue<NewsModel> minuteRingQueue = new MinuteQueue<NewsModel>();
    //2.Open thread.
    var lstTasks = new List<Task>
    {
        Task.Factory.StartNew(minuteRingQueue.Start)
    };
    //3.Add tasks performed in different periods.
    minuteRingQueue.Add(5, new Action<NewsModel>((NewsModel newsObj) =>
    {
        Console.WriteLine(newsObj.News);
    }), new NewsModel() { News = "Trump's visit to China！" });
    minuteRingQueue.Add(10, new Action<NewsModel>((NewsModel newsObj) =>
    {
        Console.WriteLine(newsObj.News);
    }), new NewsModel() { News = "Putin Pu's visit to China！" });
    minuteRingQueue.Add(60, new Action<NewsModel>((NewsModel newsObj) =>
    {
        Console.WriteLine(newsObj.News);
    }), new NewsModel() { News = "Eisenhower's visit to China！" });
    minuteRingQueue.Add(120, new Action<NewsModel>((NewsModel newsObj) =>
    {
        Console.WriteLine(newsObj.News);
    }), new NewsModel() { News = "Xi Jinping's visit to the US！" });
    //3.Waiting for all tasks to complete is usually not completed. Because there is an infinite loop.
    //F5 Run the program and see the effect.
    Task.WaitAll(lstTasks.ToArray());
    Console.Read();
}

Models，這層就是用來在延遲任務(wù)中帶入的數(shù)據(jù)模型類而已了。自己用的時候換成任意自定義類型都可以。